Reinforcement fabrics are successfully used today in the production of advanced dielectric composites for the electrical and electronic industries. In particular, for the production of laminates, fiberglass fabric dominates the market in the reinforcement of all types of thermosetting and thermoplastic resins.
The laminates have incorporated on one or both sides a copper foil at after several processes of photography, etching, drilling, finishing becomes a well known printed circuit board In a multi-layer board, additional layers of fabric reinforced resin and additional layers of copper foil, are laminated together and undergo additional processes of photography, etching, drilling and finishing to become rather complex multi-layer printed circuit boards.
Printed circuits boards, and the laminates used for their production, are required to have superior dimensional stability, the lowest possible bow and twist and very limited and predictable movement on the X & Y axes during the successive mechanical and thermal process steps.
Currently produced reinforcement fabrics are normally of plain weave construction, and are characterized by a large number of crossovers between warp yarns and weft yams e.g. about 500 or more which was determined during the 1950's as a consequence of the technology capabilities available then, and which has remained mostly unchanged.
The yarn used) particularly fiberglass yarn, has an average number of twist per meter ranging from 12 up to 40 turns per meter. The direction of twist commonly used is Z-twist. In Z-twist the filaments assume an ascending left to right configuration, as in the central portion of the letter Z (see FIG. 1). In S-twist the filaments assume an ascending right to left configuraton, as in the central portion of the letter S (see FIG. 2).
The performance challenge comes from recent technology advances in the production of printed circuit boards (and in particular high-layer count multi-layer boards), such as build-up process, micro-vias, and laser drilling, which require higher dimensional stability of the laminate and a more evenly distributed reinforcement inside the resi matrix.
U.S. Pat. No. 5,662,990 discloses that the use of untwisted yarn in the fabric reinforcement greatly improves the performance of the resulting laminate and printed circuit board. However, even better results are further obtained by changing the fabric geometry as described herein, rather than just relying only on better characteristics of single yarns.